1. Field of the Invention
The present invention relates to an engine generator apparatus and a co generation system and more particularly, to an engine generator apparatus interconnecting with an electric power network or grid for private use generator or a small-sized cogeneration facility and a cogeneration system including the engine generator apparatus.
2. Description of the Related Art
Generator apparatuses for private use have widely been provided for emergency use in case of blackout or power failure. Recently, private use cogeneration type generator apparatuses which can be interconnected with electric power networks for improvement of the efficiency of operation are getting popular. Such a cogeneration type private use generator apparatus comprises a small generator driven by a gasoline engine or a gas engine fueled with gas fuel such as town gas.
For smooth interconnection with an electric power network, the cogeneration type generator apparatus needs to comply with the guideline for technical requirements for interconnection (issued by the Ministry of Trade) which stipulates technical standards including a range of outputs of applicable power networks and protections for the power network in case of a ground fault or short-circuit. It is necessary to cancel the interconnection with the network when the operation fails to comply with the requirements of the guideline as is regarded as a fault. As the operation has been reset to comply with the requirements of the guideline, the interconnection to the power network can be re-established.
The cogeneration system driven by a gasoline engine or a gas engine includes a controller unit for purifying the exhaust gas. More specifically, an oxygen density sensor is provided across the passage of an exhaust gas from the engine for measuring the density of oxygen in the exhaust gas which is then used for controlling the air-fuel ratio in a mixture gas supplied to the engine to theoretical air-fuel ratio for complete combustion.
When the cogeneration system having such an exhaust gas purifying apparatus encounters a fault during its operation, it cancels the interconnection with the power network and then stops the engine, thereby producing the following drawback. For normal operation, the oxygen density sensor needs to have a temperature of substantially 400xc2x0 C. At every re-start operation of the engine, a warming up for raising the temperature of the oxygen density sensor from a lower level to the operable level where the sensor is activated is required. The frequent warming up operation causes a declination in the operational efficiency. Particularly, as the engine is stopped upon temporary cancellation of the interconnection with the re-interconnection within a short interval of time, the operational efficiency will significantly be declined. Also, if a protection scheme is switched on to stop the engine at every cancellation of the interconnection, it may exert unwanted loads on the startup device or other components.
The present invention is developed in view of the above drawback and its object is to provide an engine generator apparatus and a cogeneration system which can inhibit declination in the operational efficiency due to the engine stop at the cancellation of the interconnection and reduces loads exerted on the engine startup device.
An engine generator apparatus according to the present invention is provided for interconnecting an output of a generator driven by an engine with a power network, comprising, an oxygen density sensor provided on the engine for controlling the air-fuel ratio based on its output, a means for interconnecting the output of the power generator with the power network, when the oxygen density sensor becomes its activated state, a fault detecting means for detecting a fault in the interconnection with the power network, a means for canceling the interconnection with the power network when the fault detecting means detects a fault, and resuming the interconnection with the power network when the fault is removed; and a means for stopping the engine when the interconnection is canceled for a predetermined length of time due to the fault detection.
According to the above arrangement, the engine is not stopped but operated with no load even if the interconnection with the power network is canceled, provided that the interval from the cancellation to the re-interconnection is not longer than a particular length of time. The engine stop in response to every cancellation of the interconnection can successfully be eliminated. As a result, a warming up for activating the oxygen density sensor can be carried out at a lower frequency and the exertion of undesired loads on the startup device for the engine can be avoided.
A cogeneration system according to the present invention includes an waste heat utilizing unit for utilizing waste heat produced by the operation of the engine generator apparatus and is arranged wherein the engine is started in response to a heat request received from the waste heat utilizing unit. As the engine is started by the heat request from the waste heat utilizing unit, the waste heat produced during the period before the activation of the oxygen density sensor is completed can be utilized at effectiveness.